The problem of power consumption in terminals may be a considerably important element in a broadband wireless mobile communication system compared to other systems because the mobility of terminals should be considered. A sleep mode operation between a terminal and a base station has been proposed as one of such methods for minimizing power consumption in the terminal.
In a conventional sleep mode operation, a terminal requests to enter into a sleep mode if there exists no more traffic to be transmitted and/or received to and/or from a base station while performing a communication with the base station in an active mode, and receives a response to that request from the base station to change the state thereof to a sleep mode.
The terminal that has entered into a sleep state receives a message indicating whether there exists a traffic transferred from the base station during a sleep listening window, and determines that there exists no data traffic transmitted to a downlink, and increases the current sleep cycle twice if negative indication indicating that there exists no traffic is received.
Furthermore, if positive indication is received from the base station during the listening window, then the terminal determines that there exists data traffic transferred to a downlink, and initializes the current sleep cycle.
However, the power level of the terminal is increased during the set window even though there exist no protocol data unit (PDU) transferred to from the base station to the terminal during a listening window of the sleep mode, thereby causing unnecessary power consumption.